While Virgin Galactic's public sights are set on offering suborbital space tourist treks on its SpaceShipTwo passenger ships, the company is already quietly eyeing the next step: orbital space travel.

Virgin Galactic founder and president Sir Richard Branson publicly admitted the company's orbital aims last month at the dedication of the Spaceport America facility under construction in New Mexico. But he and other Virgin execs are keeping mum on the details.

"Obviously, we want to move on to orbital after we've got suborbital under our belts, and maybe even before that," Branson said.

In the last few weeks, Virgin Galactic and the Mojave, Calif.-based aerospace company Scaled Composites have flown several solo glide tests of SpaceShipTwo, most recently on Nov. 17, setting the stage for the first rocket-powered launch trials to follow. Scaled Composites built the first SpaceShipTwo for Virgin Galactic, as well as the spaceliner's prize-winning predecessor SpaceShipOne.

But how Virgin Galactic plans to take the major step of reaching orbit — and when it plans to do so — remain to be seen.

Suborbital vs. Orbital

SpaceShipTwo is a reusable space plane built to be will be carried skyward by a larger mothership jet, called WhiteKnightTwo. The smaller plane would then be dropped in midair and fire its rocket engines to push up to space. [Gallery: First Solo Flight of SpaceShipTwo]

Since it stops short of making a full orbit around Earth, SpaceShipTwo is known as a suborbital vehicle. The spacecraft will offer passengers a few minutes of weightlessness and a view of Earth from above before gliding back down to the ground.

While such a feat is no cakewalk, achieving orbital space travel is much more difficult.

Staying in space for a full orbit requires a significant velocity boost above that required for suborbital trips. Such an increase in speed, of course, requires a corresponding increase in energy, which means the craft will have to carry a lot more fuel. This extra fuel would push the spacecraft's weight up significantly, thus requiring even greater thrust to get off the ground.

Furthermore, the return trip presents a challenge.

The higher up a craft starts its descent from, the more it will accelerate as it travels back to Earth. And when a fast-moving spaceship plunges through our planet's atmosphere, it creates incredible friction and heat.

Orbital spacecraft require stronger heat shields to withstand this blast than the comparatively slow-moving suborbital craft. (The failure of the heat shield is what doomed the space shuttle Columbia during its return trip in 2003).

Branson said Virgin Galactic will aim to win a NASA contract to carry astronauts to the International Space Station, under the new space agency plan to use commercial spaceships for low-Earth orbit transportation after the space shuttles retire next year.

"Virgin Galactic is going to put forward proposals, and we plan to start work on an orbital program quite quickly," Branson said during the Oct. 22 spaceport dedication.

They'll face steep competition: No fewer than four companies, including Lockheed Martin, Boeing, SpaceX and theSierra Nevada Corporation, have made their orbital spaceship aims public. Each has said they plan to compete for a NASA contract, as well as pursue space tourism. [Top 10 Private Spaceships]

While most are gumdrop-shaped capsule designs similar to the Apollo and Soyuz capsules, Sierra Nevada's entry is a space plane. All of these would ride atop separate rockets to orbit.

Virgin Galactic has not yet shared any hints about its orbital spacecraft design, though more information will be revealed in the coming months, Branson said.

So far, besides NASA, the only other major customer for such orbital flights would be Bigelow Aerospace, a Las Vegas-based company that is constructing modules to build a commercial space station. The Bigelow space stationcould serve as a space hotel, or be rented out to other countries who would like develop their space programs, or to private research firms.

All such uses would require an orbital vehicle to assemble the station, and to transport visitors to and from it.

The sky's not the limit

Even if Virgin Galactic manages to achieve orbital space travel, the company doesn't plan to stop there.

"We'll start with suborbital flights into space, we're then dreaming about trying to move on to orbital, and dreaming about, you know, looking at maybe having hotels in space one day, dreaming about maybe having intercontinental flights," Branson said in a recent Virgin Galactic video. "And if you don't dream you don't achieve anything. We try to inspire our engineers and technicians to make dreams become realities."

Intercontinental flights, or so-called point-to-point travel, is a goal that Virgin could achieve with SpaceShipTwo and similar vehicles.

The idea is to launch from a spaceport in, say, New Mexico, but instead of landing where you started, land halfway around the world, in Sweden or Japan, for example.

"We'd love to make it a possibility," Branson said, saying such trips would travel at many times the speed of the Concord, the supersonic plane that was able to cross from New York to Paris in about 3 1/2 hours (commercial jets take around 8 hours).

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Clara Moskowitz

Clara has been SPACE.com's Assistant Managing Editor since 2011, and has been writing for SPACE.com and LiveScience since 2008. Clara has a bachelor's degree in astronomy and physics from Wesleyan University, and a graduate certificate in science writing from the University of California, Santa Cruz. To find out what her latest project is, you can follow Clara on Google+.